Summary
Highlights
Just as human cells require a circulatory system for glucose and oxygen, plant cells need a vascular system to transport water, minerals, and glucose. Water and minerals are absorbed from the soil by roots, while glucose is produced in leaves through photosynthesis. The vascular tissue, consisting of xylem and phloem, facilitates this transport.
Xylem is responsible for transporting water and minerals from the roots throughout the plant. It's often visible as the heartwood and sapwood in a fallen tree. Xylem consists of tracheids, vessels, fiber, and parenchyma. Tracheids have pitted walls, while vessels are long, hollow tubes providing continuous water flow. Fiber cells offer support, and parenchyma (the only living cells in xylem) store food. Lignin strengthens xylem cells, with patterns varying by location.
Phloem transports manufactured food, like sucrose and amino acids, from green parts of the plant (e.g., leaves) to other parts in a process called translocation. Phloem is composed of sieve tubes, companion cells, fiber, and parenchyma. Sieve tubes are elongated, thin-walled cells with perforated walls, containing a thin layer of cytoplasm to conduct food. They rely on companion cells, which have abundant cytoplasm and a nucleus, to carry out vital functions. Phloem fiber cells provide structural support, and parenchyma stores food. Only the fiber cells in phloem are dead.
The arrangement of vascular tissue differs across plant parts. In the root of herbaceous dicots, xylem forms an 'x' shape in the center, encircled by phloem. In stems, xylem and phloem are clustered in circular shapes near the edge. In leaves, xylem and phloem are found in vascular bundles, with xylem positioned above the phloem.